3-T MRI-based adaptive brachytherapy for cervix cancer: treatment technique and initial clinical outcomes.

ABSTRACT

PURPOSE: To report the techniques and initial clinical outcomes for MRI-based adaptive brachytherapy (MRIB-ABT) using 3-T MRI. METHODS AND MATERIALS All patients who underwent MRIB-ABT between January 2008 and June 2012 for cervical cancer using 3-T MRI for at least three fractions were retrospectively reviewed. The institutional standard for initiation of brachytherapy planning was 100% of dose at point A and 160% at the vaginal surface with five fractions of 500-550 cGy at Point A. The dose distribution was modified to enhance coverage of the high-risk clinical target volume (HR-CTV) and to spare the organs at risk (OAR) by altering dose specification distances around the tandem and the percentage of the Point A dose around the ring or ovoids. RESULTS: Eighteen patients (FIGO stages IB = 4, II = 12, III = 1, and IVA = 1) underwent eighty-two 3-T MRI-based insertions. All patients received 3D conformal, external beam radiation (45-50.4 Gy). The median gross tumor volume pretreatment was 38 cm(3) (2-165 cm(3)) compared with 4.8 cm(3) (1-9 cm(3)) at the first high-dose rate fraction with a median volume reduction of 88%. Dose specification at the level of Point A was altered in 51% of 3-T MRI fractions from the standard 20 mm (range, 14-18 mm) and in 8% at the ring surface to optimally cover the HR-CTV and spare the OAR. The 2-year local control, disease-specific survival, and overall survival are 100%, 100%, and 93%, respectively. CONCLUSIONS: MRIB-ABT using 3-T MRI for treatment of cervix cancer allows for customized alterations in dose specification that minimize dose to the OAR and maximize coverage of the HR-CTV.